Adhesive having insulative properties

ABSTRACT

An improved adhesive composition having increased insulative properties is provided. The adhesive composition having improved insulative properties includes a starch component; an alkaline component; sodium tetraborate; water; and a plurality of expandable microspheres. Products having improved insulation capabilities and methods of making the products having improved insulation capabilities are also provided. The present adhesive and products including the adhesive is environmentally friendly.

FIELD OF THE INVENTION

The present invention relates to an adhesive composition having improvedinsulative properties. In particular, the invention includes an adhesivecomposition and method of making an adhesive composition for use inproviding insulation to paper products, including corrugated products.

BACKGROUND OF THE INVENTION

Paper board, including corrugated paper board, is commonly used toprovide insulation for various products, including paper cups.Traditionally, corrugated paper board is prepared by first forming acorrugated element, or “medium”, by passing a cellulosic sheet betweencorrugating rolls forming a substantially sinusoidal or serpentinecross-section in the sheet. The tips of the sinusoidal portion arereferred to as flutes. An adhesive is commonly applied to the tips ofthe flutes, and a noncorrugated or planar cellulosic liner is appliedagainst the adhesive coated flutes of the corrugated elements as thecorrugated sheet passes between a corrugating roll and a pressure roll.A resulting paper product having the corrugating medium on one side andthe planar liner on another side is called a single-faced web. Thesingle-faced element may be used as is in certain applications as aliner or buffer material within a container. In some products, theadhesive is also applied to the flute tips of the single-faced web and asecond liner sheet is subsequently applied to the fluted medium in a“double faced” operation. The second liner sheet is exposed toconditions of heat and pressure during its contact with the adhesive. Inpractice, the sheet of corrugated cardboard most frequently encounteredhas two plane sides placed on each side of the corrugated medium.Depending on the specific strength desired, a sheet of corrugated boardmay also be provided with a more complex structure, such as twocorrugated mediums and three plane surfaces, two outer ones and oneinner one separating the two corrugated medium.

Starch-based adhesives are most commonly used in the corrugating processdue to their desirable adhesive properties, low cost and ease ofpreparation. The most fundamental starch corrugating adhesive, commonlyreferred to as a “Stein-Hall” formulation, is an alkaline adhesive thatis comprised of raw, ungelatinized starch suspended in an aqueousdispersion of cooked starch. The adhesive is produced by gelatinizingstarch in water with sodium hydroxide (caustic soda) to yield a primarymix of gelatinized or cooked carrier, which is then slowly added to asecondary mix of raw (ungelatinized) starch, borax and water to producethe fully formulated adhesive. In conventional corrugating processes,the adhesive is applied to the tips of the fluted paper medium orsingle-faced board, whereupon the application of heat and pressurecauses the raw starch to gelatinize, resulting in an instantaneousincrease in viscosity and formation of the adhesive bond.

While typical adhesives are sufficient to adhere the various layers ofthe insulating paper together, these adhesives do not act as insulationthemselves. Thus, in typical situations, there is required at least twolayers of paper (the liner and the medium), and in many situations threelayers are required (two liners and the medium). To achieve properinsulation, typical insulating products require the medium to have afairly high amplitude in its wave pattern, requiring more paper to beused in formation of the medium. These typical formulations result in atremendous amount of paper to be used for the product, which not onlyadds cost to the production but also is not environmentally sound.

The present invention seeks to improve insulating papers, through theuse of an adhesive composition that adds insulative properties to theproduct. In addition, the adhesive and the products made therefrom aremade from natural components and are environmentally conscious. Thepresent invention provides an environmentally sound insulating adhesivethat provides sufficient adhesion to the product upon which it is beingapplied.

SUMMARY OF THE INVENTION

The present invention relates to a starch composition and method ofusing the starch composition, which provides a greater insulation whilemaintaining sufficient strength of the adhesive. The present inventionbalances the curing properties of the starch composition with theexpansion properties of an insulating component to provide a suitableadhesive. In particular, the starch composition is selected to havegelatinization and cure temperatures, which also allow for sufficientexpansion of the insulating component, to maximize the benefits of bothadhesive strength and insulative properties.

In a first embodiment of the present invention, there is provided anadhesive composition having improved insulative properties, including astarch component; an alkaline component; sodium tetraborate; water; anda plurality of expandable microspheres, where the starch component isselected to permit full gelatinization of the starch component at atemperature at or greater than the temperature at which the expandablemicrospheres expand.

Another embodiment of the invention provides a method of preparing acorrugated product having improved insulative properties, including thesteps of: providing a substantially flat paper liner having a first sideand second side; providing a paper liner having a plurality of fluteseach having a peak and a trough; preparing an adhesive compositionhaving improved insulative properties, including the steps of: combiningthe high amylose starch component, an alkaline component, a crosslinker,and water to form a starch mixture, and then cooking the high amylosestarch mixture to form a cooked starch mixture; adding an unmodifiedstarch component to the cooked starch mixture; and adding a plurality ofexpandable microspheres to the cooked starch mixture; applying theadhesive composition to a tip of each of the flutes; mating the peaks ofsaid flutes with a surface of the first side of the planar paper linerto form a composite structure where the first paper liner and the secondpaper liner contact each other at the peaks of the flutes; curing theadhesive composition in the composite structure to a first temperatureand to a second temperature, where the first temperature and the secondtemperature differ by about 20° F. to about 40° F.

Still another embodiment of the invention provides a method of making aninsulative sheet, including the steps of: providing a substantially flatpaper sheet having a first side and a second side, the first side havinga surface with a sufficient structure to accommodate an insulatingcomponent; preparing an adhesive composition including the steps of:combining the high amylose starch component, an alkaline component, acrosslinker, and water to form a starch mixture, and then cooking thehigh amylose starch mixture to form a cooked starch mixture; adding anunmodified starch component to the cooked starch mixture; and adding aplurality of expandable microspheres to the cooked starch mixture;applying the adhesive composition to the first side of the substantiallyflat paper sheet to form a sheet with an applied adhesive composition;heating the sheet with an applied adhesive composition to a firsttemperature sufficient to expand the expandable microspheres; andheating the sheet with an applied adhesive composition to a secondtemperature sufficient to fully cure the adhesive composition.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts the results of testing conducted on various adhesives,showing the adhesion as compared to the expansion of the microspheres.

FIG. 1A is one embodiment of an apparatus for making corrugated board.

FIG. 2 is a close up cross sectional view of a corrugated board thatdoes not include expandable microspheres.

FIG. 3 is a close up cross sectional view of a corrugated board thatincludes expandable microspheres.

FIG. 4 is a close up cross sectional view of a corrugated board thatincludes expandable microspheres.

DETAILED DESCRIPTION OF THE INVENTION

Typical adhesives for use in insulating paper products providenegligible, if any, insulating properties to the end product. Theseadhesive are generally useful only for adhering a liner (or liners) tothe medium, allowing the air space between the tip of the flute and theliner to achieve the insulation. Further, since the adhesive compositiononly provides adhesion between the flute tip and the liner, there isvery little space between the flute tip and the liner at the point ofadhesion. The lack of space between these two elements at the point ofadhesion provides very little, if any, added insulation. Since air isthe primary means of insulation, the amplitude of the wave formation ofthe medium must be significant, which requires that the medium be madeof a sheet of paper that is quite large. Further, to provide sufficientinsulation, such typical products usually use thick layers of paper toform the liner(s), or alternatively use multiple layers of paper to formone liner. As a result, typical processing of such products is not onlyan expensive manufacturing process, but also results in a great deal ofwaste.

The present invention provides an adhesive composition that providesinsulative properties to the product on which it is used. The adhesivecompositions described herein may be useful in traditional corrugatedpaper board products having a medium and either one or two liners.Through the use of the inventive adhesive composition, a greaterinsulation space may be provided between the flute tip of the medium andthe liner to which it is attached at the point of adhesion. In alternateembodiments, the inventive adhesive composition may be useful in forminga paper board insulation that avoids the need for a medium, insteadrelying upon the adhesive composition itself to provide the desiredinsulation. The adhesive composition described herein is substantiallymade from natural, biodegradable materials, and the products made withthe inventive adhesive composition require less paper to form. The endresult is a less expensive and more environmentally conscious product.The insulating products useful herein include paper products forconsumer use, such as for hot drinking cups, hot food containers, andthe like.

The present invention is based on the discovery that an adhesivecomposition for use in preparing insulating products may include aplurality of expandable microspheres therein. When these expandablemicrospheres are allowed to expand in an adhesive composition, theycreate a foam-like adhesive material, which provides added insulation tothe product. For example, when the adhesive is applied between the linerand the tip of a flute of a medium, the expandable microspheres may beexpanded, thereby providing an insulating space between the flute tipand the liner at the point of attachment. This insulated space adds tothe insulative properties of the product formed, allowing for a mediumhaving a smaller amplitude between waves to be used (i.e., requiringless air space), and yet still provide adequate insulation. The mediumlayer may have a flatter wave configuration, resulting in less paperused in the medium. In addition, the added insulation allows the productto use thinner paper and/or single-layered paper liners, resulting inless cost and less wasted materials.

In a first embodiment, the invention includes an adhesive for preparingan insulating board, such as corrugated or uncorrugated paper board. Thepaper board may be made from any type of paper material, includingcellulosic paper materials traditionally used in insulating products.Desirably, the paper products used are recyclable materials.

The adhesive composition may be made from any number of materials.Desirably, the adhesive composition includes water, a starch component,a crosslinker component, an alkaline component, and a plurality ofexpandable microspheres. The adhesive composition may further includeone or more humectants, preservatives, or fillers. Other materials thatdo not adversely affect the adhesive and insulating properties of theadhesive composition may be used as desired.

The adhesive composition may include any polar solvent, particularlywater, in the formulation. In a desired embodiment, prior to setting (orgelatinizing) the composition, the adhesive composition includes thepolar solvent in an amount of about 40% to about 75% by weight of theadhesive composition prior to setting of the composition, and mostdesirably from about 50% to about 70% by weight of the composition priorto setting of the composition.

The adhesive composition includes a starch component. The starchcomponent may be present in the adhesive composition in any amount, anddesirably is present in an amount of from about 20% to about 40% byweight of the adhesive composition prior to setting of the composition,and more desirably from about 25% to about 35% by weight of the adhesivecomposition prior to setting of the composition. The starch componentmay include any desired starch materials, particularly starch materialsderived from natural sources, including, for example, corn. In someembodiments, the starch component may include starch having a highlybranched composition. For example, the starch component may includeunmodified starch or “pearl” starch. As used herein, the term“unmodified” starch refers to a starch composition having less than 25%amylose content. The unmodified starch may be used in any form, and ispreferably used in powdered or granulated form having a diameter ofabout 20 microns. In other embodiments, the starch component may includea cooked starch, also referred to as a carrier starch. The cooked starchmay have a higher viscosity than the unmodified starch.

In still other embodiments, the starch component may include a starchmaterial having a composition with a higher concentration of straightchain materials. Such components may include a high amylose starchmaterial, including that sold by Henkel Corporation under the trade nameOptamyl®. As used herein, a starch having a high amylose content(referred to as “high amylose starch”) includes at least 50% amylosecontent. In some embodiments, a high amylose starch may have betweenabout 25% to about 50% amylose, and more desirably between about 35% and50% amylose concentration. As will be explained below, in oneembodiment, the use of a high amylose starch material in combinationwith an unmodified starch material may be beneficial to the expansion ofmicrospheres in the adhesive composition. The combination of highamylose starch and unmodified starch results in a starch component thathas a higher moisture content and a higher final setting (or curing)temperature.

In embodiments where the starch component includes a combination ofmaterials, the starch component includes a mixture of unmodified starchand at least one of cooked starch or a high amylose starch. Desirably,the starch component includes a mixture of unmodified starch and highamylose starch. The unmodified starch component may be from about 60% toabout 90% by weight of the starch component. In preferred embodiments,the unmodified starch component and the high amylose starch componentare present in a ratio of from about 5:1 to about 3:1.

The adhesive composition may include one or more alkaline components.The alkaline component may be present in an amount of from about 0.5% toabout 1.5% by weight of the adhesive composition prior to setting of thecomposition. The alkaline component may include any component having analkaline nature. In particular embodiments, the alkaline componentincludes sodium hydroxide, however, any desired alkaline component maybe used as desired.

The adhesive composition may include one or more crosslinkingcomponents. Crosslinkers useful in the present invention may include,for example, sodium tetraborate (also referred to as Borax).Crosslinkers may be present in the invention in an amount of from about0.10% to about 0.20% by weight of the adhesive composition prior tosetting of the composition.

The adhesive composition may include any optional components, includinghumectants, preservatives, or fillers. Humectants useful in the presentinvention aid in maintaining viscosity stability of the composition, andmay include, for example, glycerol, glycerine, urea, propylene glycol,glyceryl triacetate, sugars and sugar polyols such as sorbitol, xylitol,and maltitol, polymeric polyols such as polydextrose, natural extractssuch as quillaia or lactic acid, or any other desired composition havinghumectant properties. Humectants may be useful in the present inventionin an amount of from about 0.1% to about 15% by weight of the adhesivecomposition prior to setting of the composition. Preservatives may beuseful in the present invention, and include preservatives such as1,2-benzisothiazolin-3-one. Preservatives may be used in the amount offrom about 0.05% to about 0.20% by weight of the adhesive compositionprior to setting of the composition. Any desirable fillers may be usedas are known in the art.

The adhesive composition includes a plurality of expandablemicrospheres. The expandable microspheres useful in the presentinvention should be capable of expanding in size in the presence of heatand/or radiation energy (including, for example, microwave, infrared,radiofrequency, and/or ultrasonic energy). The microspheres useful inthe present invention include, for example, heat expandable polymericmicrospheres, including those having a hydrocarbon core and apolyacrylonitrile shell (such as those sold under the trade nameDUALITE®) and other similar microspheres (such as those sold under thetrade name EXPANCEL®). The expandable microspheres may have anyunexpanded size, including from about 12 microns to about 30 microns indiameter. In the presence of heat, the expandable microspheres of thepresent invention may be capable of increasing in diameter by about 3times to about 10 times. That is, the diameter of the expandablemicrospheres may be expandable to about 300% of the starting diameter toabout 1,000% of the starting material, and most desirably, the diameterof the expandable microspheres may be expandable from about 350% toabout 600% of the starting diameter. Upon expansion of the microspheresin the adhesive composition, the adhesive composition becomes afoam-like material, which has improved insulation properties. It may bedesired, as will be explained below, that the expansion of themicrospheres takes place in a partially gelatinized adhesivecomposition.

The expandable microspheres have a particular temperature at which theybegin to expand and a second temperature at which they have reachedmaximum expansion. Desirably, the temperature at which thesemicrospheres begin to expand (Texp) is from about 180° F. to about 210°F., and more desirably from about 190° F. to about 208° F. Thetemperature at which the microspheres have reached maximum expansion(Tmax) is desirably from about 250° F. to about 285° F., and moredesirably from about 257° F. to about 275° F. Of course, differentgrades of microspheres have different Texp and Tmax. For example, oneparticularly useful microsphere has a Texp of about 208° F. and a Tmaxof about 275° F., while another useful microsphere has a Texp of about190° F. and a Tmax of about 266° F. While any particular grade ofmicrospheres may be used in the present invention, the process should beslightly modified to account for the Texp and Tmax of the microspheres.

Although the choice of the particular microspheres and their respectiveTexp and Tmax is not critical to the invention, the processingtemperatures may be modified depending upon these temperatures. In mostapplications, it is desirable that the Tmax for the microspheres be atemperature that is equal to or lower than the full setting (or curing)temperature of the starch adhesive composition. As can be appreciated bythose of skill in the art, the inventive adhesive composition includes aplurality of unexpanded microspheres in a fluid starch-based adhesivecomposition. Before the adhesive composition is fully set or cured,these microspheres are able to move within the composition and are ableto expand. Once the adhesive composition is set, however, themicrospheres are substantially locked in place, making expansion thereofdifficult, if not impossible. For this reason, it is useful that themaximum expansion temperature of the microspheres (Tmax) be equal to orlower than the complete setting temperature of the adhesive composition.

Of course, it may be noted that the starch-based adhesive compositionwill begin to set, or gelatinize, at a lower temperature than the fullcure temperature. In some embodiments, the initial setting temperatureof the starch composition may be from about 138° F. to about 156° F.Although the starch adhesive will begin to gelatinize at thistemperature, the adhesive composition may still have a high moisturecontent and will be substantially fluid. The temperature at which thestarch adhesive composition fully sets is desirably equal to or higherthan the Tmax of the expandable microspheres, however the temperature atwhich the starch adhesive composition fully sets may be between the Texpand Tmax of the microspheres.

It may be desired that the maximum expansion temperature of themicrospheres (Tmax) and the final setting temperature of the adhesivecomposition differ by about 20° F. to about 40° F., and more desirablyabout 30° F. This difference allows for the expandable microspheres tobe expanded and for the adhesive to be properly set. Desirably, thetemperature at which the adhesive begins to gelatinize may be about 20°F. to about 40° F. lower than the Texp of the microspheres, and moredesirably about 30° F. lower than the Texp of the microspheres, and thetemperature at which the adhesive is fully set may be about 20° F. toabout 40° F. higher than the Tmax of the microspheres, and desirablyabout 30° F. higher than the Tmax of the microspheres.

In a particularly desirable embodiment of manufacturing products, theadhesive composition may be applied to the surface (or surfaces) of aproduct and subjected to heat sufficient to begin gelatinization of theadhesive. Beginning the gelatinization of the adhesive may aid inholding the adhesive and microspheres in place, but will allow themicrospheres the freedom to expand. The heat may then be raised to atemperature sufficient to expand the microspheres. Finally, and the heatmay be raised again to a temperature sufficient to fully set theadhesive composition. Heat may be applied by any desired method,including in an oven or through the use of heated rollers. It should benoted that the various stages (beginning gelatinization, expansion ofthe microspheres, and full setting of the adhesive) may be achieved byradiation energy, either as a replacement for or in addition to directheat. That is, for example, the various steps may be achieved by use ofmicrowave or radiofrequency radiation, for example. In addition, theprocess may include any combination of heat application and radiationapplication. For example, the beginning gelatinization of the adhesivecomposition may be achieved through direct heat, while the expansion ofthe microspheres may be achieved through application of radiationenergy.

In some embodiments, the starch component of the adhesive compositionincludes a combination of unmodified starch and high amylose starch.This combination of starches results in a composition having a highermoisture content, and thus a higher final setting temperature. Althoughthe beginning gelling temperature of the adhesive may remain about thesame temperature, the final setting temperature may be higher than withunmodified starch alone. The present inventors have discovered that, byincreasing the set temperature of the adhesive composition, a greaterwindow of temperatures may be provided at which to expand themicrospheres. Other additives may be included in the composition toincrease the setting temperature of the adhesive as desired.

The adhesive composition includes a plurality of unexpended, expandablemicrospheres. Depending upon the particular expandable microspheres usedin the composition, the desired amount of the microspheres in thecomposition may be modified. It has been discovered by the presentinventors that if the adhesive composition includes too high aconcentration of expandable microspheres, there will be insufficientadhesion upon expansion of the microspheres. However, if there is toolow a concentration of expandable microspheres, there will beinsufficient expansion of the resulting adhesive and thus insufficientinsulation. Therefore, consideration of the loading level and theexpansion ratio, as well as the expansion ratio and the temperature atthe loading level, must be taken into account when determining theoptimal concentration of expandable microspheres in the composition. Ifthe expansion ratio of the microspheres is lower, there may be a higherconcentration in the adhesive composition, and conversely, if theexpansion ratio of the microspheres is higher, there may be a lowerconcentration in the adhesive composition.

In preferred embodiments, it is desirable that the expandablemicrospheres be present in the adhesive composition in an amount of fromabout 0.5% to about 5.0% by weight of the adhesive composition prior tosetting of the composition, and more desirably from about 1.0% to about2.0% by weight of the adhesive composition prior to setting of thecomposition, and most desirably at about 1.2% by weight of the adhesivecomposition prior to setting of the composition. For an embodimentincluding expandable microspheres that have a diameter expansion ratioof about 370% at Tmax, the microspheres may be present in an amount ofabout 1.5% to about 2.0% by weight of the adhesive composition prior tosetting of the composition. For an embodiment including expandablemicrospheres that have a diameter expansion ratio of about 470% at Tmax,the microspheres may be present in an amount of about 1.0% to about 1.5%by weight of the adhesive composition prior to setting of thecomposition. In systems where there are lower heating capabilities, itmay be desirable to include a higher concentration of expandablemicrospheres, such as up to 4% by weight of the adhesive compositionprior to setting of the composition. The expansion ratio of theexpandable microspheres and the loading level of the microspheres willbe related to each other. As set forth in FIG. 1, the Applicant hastested several different grades of expandable microspheres,demonstrating the concentration of the microspheres in various adhesivecompositions that falls within the “danger zone” (loss of adhesion) andthe “safe zone” (good adhesion). Desirably, the concentration of themicrospheres in the adhesive composition should fall between these twozones. This balances expansion, and thus insulation, with adhesion ofthe resulting foam-like adhesive.

The present invention provides a method of preparing an adhesivecomposition having improved insulation properties. The method includesfirst combining a starch component, alkaline component, crosslinkers,polar solvent, and optional humectants, preservatives, or fillers toform a starch mixture. Once the starch mixture is formed, it may bepartially gelatinized to form a gelatinized starch mixture, and then theplurality of expandable microspheres may be added to the gelatinizedstarch mixture. If desired, the plurality of expandable microspheres maybe added to the starch mixture prior to beginning gelatinization. Insome embodiments, the starch component may include a combination ofunmodified starch and high amylose starch. In such embodiments, it maybe preferable to combine the high amylose starch component, alkalinecomponent, crosslinker, polar solvent, and optional humectants,preservatives and fillers, gelatinize this mixture, and then separatelyadd the unmodified starch component. Once this mixture is achieved, theplurality of expandable microspheres may be added.

In other embodiments, the present invention provides a kit for providingan adhesive composition having improved insulation properties. In thisembodiment, the kit includes two parts, a first part and a second part,which are desirably stored in separate containers. The first partincludes a starch adhesive component, including the starch component,alkaline component, crosslinker, polar solvent, and optional humectants,preservatives, or fillers. The first part may be partially gelatinizedif desired, providing increased viscosity to the first part. The secondcomponent includes the plurality of expandable microspheres. The secondpart may include the microspheres in any form, such as dry powder,slurry, or any desired form. The kit may further include a means forcombining the two parts together to form the adhesive composition havingimproved insulation properties, such as a separate container into whicheach of the first and second parts may be fed. If desired, the kit mayfurther include instructions for use in preparing the adhesivecomposition.

The present invention is further related to an insulated corrugatedboard. Any known process of forming corrugated board may be used, andFIG. 1A depicts one embodiment of an assembly useful in forming thecorrugated board. Desirably, the board is made of paper that has areduced thickness when compared to traditional insulating corrugatedboards. Any type of paper may be used in the invention, for example, thepaper may have a thickness of from about 0.0036 inches to about 0.0052inches in thickness. In addition, it is desirable to use lower weightpaper than that which is traditionally used in insulating products.Traditional insulating products generally use “33#” paper for thevarious paper components. It is desirable to use paper that is of alower weight than “23#” paper, and more desirably it is desirable to use“18#” paper for the various components of the corrugated board. That is,the various components (including liner(s) and medium) desirably includepaper that is known as 18# paper (0.0036 inches in thickness, density ofabout 67.72 g/m2).

The insulated corrugated board may be single faced or double faced.Single faced corrugated boards include a single paper liner, which is asubstantially flat paper liner having a first side and a second side,and a medium, which is a paper liner having a first side and second sidethat has been formed into a sinusoidal wave configuration having aplurality of flutes on each side. In this embodiment, the first side ofthe paper liner is secured to the tips of the flutes on the first sideof the medium. A double faced corrugated board further includes a secondpaper liner, which is a substantially flat paper liner having a firstside and a second side, where the first side of the second paper lineris secured to the tips of the flutes on the second side of the medium.Although the below description of the board and the methods for makingsuch boards are generally directed to single faced boards, it is to beunderstood that the invention further relates to double faced boards,which may be achieved by including a second liner either at the time ofprocessing the first liner or after the first liner has been adhered.

The inventive corrugated board of the present invention includes theinventive adhesive described above. The inventive adhesive, includingthe starch component, alkaline component, crosslinker, polar solvent,plurality of expandable microspheres, and optional humectants,preservatives, or fillers is applied to the tips of the flutes of themedium. In one embodiment of the invention including a high amylosestarch component and unmodified starch component, the high amylosestarch component, an alkaline component, a crosslinker, and water arecombined to form a starch mixture, and then the high amylose starchmixture is cooked to form a cooked starch mixture. Next, an unmodifiedstarch component may be added to the cooked starch mixture, and aplurality of expandable microspheres are added to the cooked starchmixture. Alternatively, the adhesive components may be simply addedtogether.

If a single faced corrugated board is desired, the adhesive compositionis applied to the tips of the flutes of only one side of the medium, andthe first side of one paper liner is applied thereon. If desired, theadhesive composition is partially gelatinized. The expandablemicrospheres are allowed to expand and then the adhesive composition isset in place. The resulting corrugated board thus has an insulatingspace between the surface of the paper liner and the tips of the flutesof the medium at the point of adhesion. The corrugated board desirablyhas an insulating space between the paper liner and the tips of theflutes at the point of adhesion in the amount of about 0.01 inches. Itshould be understood, of course, that the particular increase indistance between the flute tips and the liner is not critical, and thata small increase in distance may generate a significant amount of addedinsulation. In desired embodiments, the space between the flute tip andthe release liner in the present invention may be greater than thedistance between flute tip and liner without expanded materials. At thesame time, the desired increased distance between the flute tip and theliner should not be so great as to be detrimental to the bond strengthbetween the two.

If a double faced corrugated board is desired, the adhesive compositionis applied to the tips of the flutes of the second side of the medium,and a second paper liner is applied thereon. Similarly, the adhesive ispartially gelatinized, the expandable microspheres are allowed to expandand then the adhesive composition is set in place. The resultingcorrugated board thus has an insulating space between the surface of thepaper liner and the tips of the flutes of the medium. The corrugatedboard desirably has an insulating space between the paper liner and thetips of the flutes at the point of adhesion in an amount that is greaterthan the space traditionally seen with conventional adhesives. In oneembodiment, the increase in space between the two generated by theexpanded microspheres is about 0.001 inches.

The present invention is not limited to single or double facedcorrugated board, and may be used in a number of applications. Otherapplications in which the invention is useful include doublebackcorrugator formulations with higher viscosity, coater applications withlower viscosity, and the like.

It is particularly preferred that the medium layer have a reducedamplitude as compared to traditional corrugated boards. Through the useof the present invention, there is an insulating space between the tipof the flute and the surface of the liner at the point of contact, whichprovides added insulation. This added insulation reduces the need for asmuch air space between the flutes on the second side of the medium andthe paper liner. In a preferred embodiment, the amplitude of the mediumis about 0.04 inches as measured from the tip of adjacent flutes, whiletraditional mediums have a flute wavelength of from 0.063 to about0.134. Thus, in one embodiment, the invention provides a corrugatedboard that has a medium having a reduced wavelength, where the reducedwavelength is about 0.02 to about 0.09 inches less than traditionalcorrugated boards.

It has been discovered that through the use of the present adhesivecomposition, and reducing the amplitude of the medium reduces theoverall amount of paper used in the corrugated board by about 20% ascompared to traditional corrugated boards. In addition, the addedinsulation allows for insulating products to be formed with thinnerpaper liners and mediums, again resulting in reduced cost and alsoreduced waste.

The present invention further provides a method of forming a corrugatedboard having improved insulative properties. As explained above, thepresent inventors have discovered that the adhesive composition mustbalance the setting temperature of the starch-based adhesive with theexpansion temperature of the expandable microspheres used therein. Inthe inventive method, a first substantially flat paper liner having afirst and second side is provided. The first paper liner has a thicknessof from about the paper may have a thickness of about 0.0036 inches toabout 0.0052 inches in thickness, which is thinner than traditionalpaper liners used in corrugated boards, which traditionally have athickness of about 0.0062 inches. A second paper liner having a firstand second side is provided, which is formed into a medium having asinusoidal wave including a series of flutes on each of the first andsecond sides. The medium desirably has an amplitude of about 0.04 inchesas measured from the tip of adjacent flutes, and a wavelength of about0.13 inches.

An adhesive composition is prepared. The adhesive composition may beprepared immediately prior to forming the corrugated board or it may beprepared in advance and stored until needed. The adhesive composition isprepared by combining a starch component, alkaline component,crosslinker, polar solvent, and optional humectants, preservatives, orfillers to form a starch mixture, and partially gelatinizing the starchmixture to form a gelatinized mixture. A plurality of expandablemicrospheres is added to the gelatinized mixture, forming the adhesivecomposition. If desired, the expandable microspheres may be added to thestarch mixture prior to partially gelatinizing the mixture.

As explained above, the starch component of the adhesive composition mayinclude an unmodified starch, cooked starch, high amylose starch, andcombinations thereof. The various components of the adhesive compositionmay be present in the adhesive composition in the amounts describedabove. In preferred embodiments, the starch component includes a mixtureof unmodified starch and high amylose starch. It is particularlypreferred that the temperature of maximum expansion of the microspheresbe a temperature that is lower than the final setting temperature of theadhesive composition, for the reasons set forth above. However, thetemperature at which the adhesive composition begins to gel or set maybe lower than the expansion temperature of the expandable microspheres.If desired, additives or other components may be added to the adhesivecomposition to raise the setting temperature thereof. It is desirablethat the full setting temperature of the adhesive be at least as high asthe Tmax of the expandable microspheres, and particularly desirable thatthe full setting temperature of the adhesive be at least 30° F. higherthan the Tmax of the expandable microspheres.

In the method of forming the corrugated board, a predetermined amount ofthe adhesive composition is applied to the tips of the flutes of thefirst side of the medium. Desirably, the adhesive composition is appliedin a relatively thin layer, the layer having a thickness of from about0.05 to about 0.07 inches. The adhesive composition may be applied inthe presence of heat and/or pressure. In one embodiment, the adhesivecomposition may be applied under a pressure of about 30 bar and as themedium is heated at a temperature of about 300° F.

After the adhesive composition has been applied to the tips of theflutes of the first side of the medium, the tips of the flutes arecontacted with the first side of the first paper liner. It is desirablethat the contacting be performed under a slight pressure, so as toeffectively join the medium and the paper liner, but excessive pressureis to be avoided (to avoid squeezing out the adhesive from the point ofcontact). At this point, an uncured corrugated product is formed, wherethe paper liner and the medium are secured to each other via theadhesive, but the adhesive has not been set. If desired, the uncuredcorrugated product may be exposed to heat and/or radiation energysufficient to begin gelatinization of the adhesive, but insufficient toexpand the plurality of expandable microspheres. Gelatinization of theadhesive may be useful in holding the various components of the productin place until final curing is established.

The uncured corrugated product is then exposed to heat (including in anoven or via contact with heated rollers) and/or radiation energy(including, for example, microwave, infrared, radiofrequency, orultrasonic energy) to expand the plurality of microspheres. In oneembodiment, the uncured corrugated product is exposed to heat at atemperature sufficient to expand at least a majority of the microsphereson the tip of one flute, but the temperature is insufficient to fullyset the adhesive composition. In another embodiment, the uncuredcorrugated product is exposed to microwave or infrared energy sufficientto expand at least a majority of the expandable microspheres, but at anenergy level that will not fully set the adhesive composition. Theresulting product is an uncured corrugated product having expandedmicrospheres.

As can be understood, at this point in the process, the microspheres atany given flute tip have expanded to form a foam-like adhesivecomposition, generating an increased space between the flute tip and thepaper liner. Thus, during the manufacturing process, it is importantthat the adhesive composition be permitted to expand and separate thefirst paper liner and the medium. That is, any pressure holding thefirst paper liner and the medium must not be so great to prohibitexpansion of the adhesive and thus separation of the paper liner and themedium. If the pressure is so great, the adhesive may expand to theside, i.e., into the air space between the medium and the paper liner.In addition, any heat and/or radiation energy applied to the productshould not be so great as to fully set the adhesive composition,allowing the microspheres to expand. It is desirable that the expandedadhesive composition be located at each of the flute tips at the pointof contact with the liner, thus providing insulation space between thefirst paper liner and the medium at the site of contact.

After expansion of the microspheres, the uncured corrugated producthaving expanded microspheres may then be exposed to heat and/orradiation energy (including microwave or infrared energy) sufficient tofully set or cure the adhesive composition. The result is a corrugatedpaper having improved insulative properties.

The method described above provides a single-faced corrugated board.However, the above method may further be used to provide a double-facedcorrugated board. In addition to the above steps, a second substantiallyflat paper liner may be provided. The second liner may be applied to thesecond side of the medium at the same time as the first liner is appliedto the first side of the medium, or the second liner may be applied tothe second side of the medium after the first liner is adhered to themedium. It may be desirable that the second liner be applied to thesecond side of the medium after the first liner has been fully adheredto the medium. The processing and setting steps as described above maybe repeated with the second liner to provide a double-faced corrugatedboard.

In some embodiments, it may be desirable to form shoulders of expandedadhesive material (also referred to as “fillets”) along the sides of theflute tips, between the flute and the liner. For example, as can be seenin FIG. 2, which is a close up cross-sectional view of an adheredcorrugated board without expandable microspheres, there is littlematerial at the sides of the flute tip. FIGS. 3-4, however, are close upcross-sectional views of an adhered corrugated board with expandablemicrospheres, which depict the presence of expanded adhesive compositionat the sides of the flute. These shoulders may aid in strength of thebond between the medium and liner, and may therefore may be desirablygenerated. However, it is of course understood that formation ofshoulders along side the flutes is not required and may not, in someembodiments, be desired.

In an alternate embodiment, there is provided an insulating paperproduct that has no medium, and a method for forming an insulating paperproduct that has no medium. As may be appreciated by those of skill inthe art, conventional corrugated insulating boards require the presenceof the medium, which has a sinusoidal wave configuration to provide anair space between the medium and the paper liner(s). The air pocketsprovide the necessary insulation. Since the medium layer constitutesmore than half of the paper of the corrugated product in a single-faceddesign, it would be particularly desirable that the medium layer beomitted. Removing the medium would result in a product that uses lessthan half of the paper traditionally required, which would significantlyreduce the cost associated with the product and also reduces the wastegenerated by more than half. However, heretofore, it has been difficultto achieve a product that has the necessary insulation without includingthe medium layer.

The present invention provides an insulative product that does notinclude a medium layer. It has been discovered that the adhesivecomposition of the present invention is capable of providing thenecessary insulation required in insulating products. In thisembodiment, there is provided an insulating sheet including asubstantially flat paper liner having a first side and a second side.The first side of the paper liner includes a plurality of expandablemicrospheres secured thereto in an adhesive composition, where theplurality of expandable microspheres has been expanded and the adhesivecomposition has been set or cured. Thus, the product includes a paperliner having an adhered, foam-like composition on the first sidethereof. The expandable microspheres include those described above, andthe adhesive composition includes the components described above,including the starch component, alkaline component, crosslinker, polarsolvent, and optional humectants, preservatives, or fillers. Asexplained above, the starch component of the adhesive composition mayinclude an unmodified starch, cooked starch, high amylose starch, andcombinations thereof.

The adhesive composition of the insulative product may be applied to thefirst surface of the paper liner in any configuration desired, includingin a series of dots, stripes, waves, checkerboard patterns, any generalpolyhedron shapes that have substantially flat bases, and combinationsthereof. Further, the adhesive composition may be applied to the firstsurface in a series of cylinders. In addition, if desired, the adhesivecomposition may be applied to the first surface as a substantially flatsheet of adhesive covering the entire first surface or covering aportion of the first surface. Optionally, a second paper liner may beapplied to the top surface of the adhesive composition, forming asandwiched configuration of: first paper liner—adhesive with expandedmicrospheres—second paper liner.

A method of forming an insulative sheet is also provided. In thismethod, there is first provided a substantially flat paper liner havinga first surface and a second surface. An adhesive composition isprepared. The adhesive composition may be prepared immediately prior toforming the insulative sheet, or it may be prepared in advance andstored until needed. The adhesive composition is prepared by combiningthe materials described above, including a starch component, alkalinecomponent, crosslinker, polar solvent, and optional humectants,preservatives, or fillers to form a starch mixture, and gelatinizing thestarch mixture to form a gelatinized mixture. In embodiments where thestarch component includes a combination of unmodified starch and a highamylose starch component, it may be desirable to partially gelatinizethe high amylose starch component, alkaline component, crosslinkers,polar solvent, and optional humectants, preservatives and fillers priorto adding the unmodified starch component. A plurality of expandablemicrospheres is added to the partially gelatinized mixture, forming theadhesive composition. If desired, the expandable microspheres may beadded to the starch mixture prior to partially gelatinizing the mixture.

As explained above, the starch component of the adhesive composition mayinclude an unmodified starch, cooked starch, high amylose starch, andcombinations thereof. The starch component desirably includes themixture of unmodified starch and high amylose starch, as explainedabove. The various components of the adhesive composition may be presentin the adhesive composition in the amounts described above. It isparticularly preferred that the temperature of maximum expansion of themicrospheres (Tmax) be a temperature equal to or lower than the fullsetting temperature of the adhesive composition. If desired, additivesor other components may be added to the adhesive composition to raisethe setting temperature thereof. It is desirable that the full settingtemperature of the adhesive be at least as high as the Tmax of theexpandable microspheres, and particularly desirable that the fullsetting temperature of the adhesive be at least 30° F. higher than theTmax of the expandable microspheres.

In the method of forming the insulative sheet, a predetermined amount ofthe adhesive composition is applied to the first surface of the paperliner. The adhesive composition may be applied in any configurationdesired, including, for example, in a series of dots, stripes, waves,checkerboard pattern, a series of polyhedrons, and combinations thereof.Further, the adhesive composition may be applied to the first surface ina series of cylinders. In addition, if desired, the adhesive compositionmay be applied to the first side as a substantially flat sheet ofadhesive, covering all or part of the first side of the paper liner. Theadhesive composition may be applied in any desired thickness, anddesirably is applied in a thickness of about 0.04 inches. In embodimentswhere the composition is applied in the form of a cylinder, it may bedesirable that the height of each cylinder is approximately the same asthe diameter of each cylinder. The cylinders may be applied to the firstsurface in any configuration, desirably each cylinder is spaced asubstantially equal distance from each other cylinder. It isparticularly desirable that the separation between adjacent cylinders isabout two times the height of the cylinders. The adhesive compositionmay be applied in the presence of heat if desired; however, it isimportant that the heat at application not be so high as to fully setthe adhesive composition.

After the adhesive composition has been applied to the first side of thepaper liner, the paper liner with wet adhesive thereon may be exposed toheat and/or radiation energy to begin to set the adhesive composition.The adhesive composition therefore locks in the components, includingthe plurality of microspheres, in place and adheres them to the surfaceof the paper liner. It may be desired to only partially set the adhesivecomposition, thereby providing a composition that locks in thecomponents and maintains them sticking to the surface of the paperliner, but is not completely set. As explained above, only partiallysetting the adhesive composition (i.e., leaving a higher amount ofmoisture in the adhesive, such as at least 10% moisture content) allowsthe expandable microspheres to expand.

After setting of the adhesive, the paper liner is then exposed to heatand/or radiation energy sufficient to expand the plurality ofmicrospheres. In one embodiment, the paper liner with wet adhesivethereon is exposed to heat at a temperature sufficient to expand atleast a majority of the microspheres. In another embodiment, the paperliner with wet adhesive thereon is exposed to microwave or infraredenergy sufficient to expand at least a majority of the expandablemicrospheres. The resulting product is a paper liner having an adhesivehaving expanded microspheres therein. The adhesive composition may thenbe exposed to heat and/or radiation energy sufficient to fully set theadhesive composition.

If desired, after application of the adhesive composition to the firstside of the paper liner, a second paper liner having a first side andsecond side may be provided and the first side of the second paper linerapplied to the surface of the applied adhesive composition, forming asandwich configuration. Thereafter, expansion of the microspheres andsetting of the adhesive may take place as explained above.

The present invention may be better understood through analysis of thefollowing examples, which are non-limiting and are intended only to helpexplain the invention.

Examples Example 1—Formation of an Adhesive with Improved InsulatingProperties

An adhesive composition was prepared having the following composition:

Component Wt. % Water (1) 17.20 Crosslinker¹ 0.14 Cooked starch 1.09Alkaline agent² 0.97 Water (2) 9.73 Water (3) 24.16 Humectant³ 10.63Unmodified starch 34.78 Preservative⁴ 0.10 Expandable microspheres⁵ 1.20¹sodium tetraborate ²sodium hydroxide, 50% FCC, Rayon ³glycerol,glycerine, USP 99.7% ⁴Proxel GXL; 1,2-benzoisothiazolin-3-one⁵Expancel ® microspheres

Water (1) was mixed with the crosslinker, and cooked starch was added.The mixture was heated in a bath at 140° F. The alkaline agent was addedto the mixture, and mixed for two minutes to form a gel. The mixture wasthen removed from the bath, and water (2) was added. The mixture wasmixed at high speed for 5-10 minutes. During this mixing process, aseparate mixture of water (3), humectant and unmodified starch weremixed until smooth. The two mixtures were combined and mixed untilsmooth. Preservatives were then added and the resulting mixture mixedfor 10 minutes. The expandable microspheres were then added and themixture mixed for 10 minutes.

Example 2—Formation of an Adhesive with Improved Insulating Properties

An adhesive composition was prepared having the following composition:

Component Wt. (lbs) Water (1) 710 High amylose starch 150 Caustic sodabeads 15 Primary Crosslinker¹ 5.5 Water (2) 1378 Secondary CrosslinkerA¹ 4 Unmodified starch 750 Secondary Crosslinker B¹ 4 Humectants² 15Expandable microspheres 36 ¹sodium tetraborate ²glycerine or urea

Water (1) is introduced into a first mixer and heated to 110° F. To thisheated water is added the high amylose starch, caustic soda beads andprimary crosslinker. In a second mixer, water (2) is introduced andheated to 98° F. Secondary crosslinker A, unmodified starch, secondarycrosslinker B and humectants are added and mixed. The two mixers arecombined and mixed. The expandable microspheres are added to theresulting mixture.

Example 3—Comparison of Various Adhesives

Four adhesive compositions were prepared (C1, C2, C3, and I), which areas follows: Composition C1 included an unmodified corn starch basedadhesive composition (Stein-Hall adhesive) without expandablemicrospheres; Composition C2 included an unmodified corn starch basedadhesive composition (Stein-Hall adhesive) with Dualite 130Wmicrospheres; Composition C3 included a starch based adhesivecomposition made from a blend of unmodified corn starch and high amylosecorn starch; and Composition I included a starch based adhesivecomposition made from a blend of unmodified corn starch and high amylosecorn starch with Dualite 130W microspheres. The adhesives were used inthe formation of corrugated rolls having different combinations of 18#,23#, and 33# paper for the liner and for the medium, and were evaluatedafter drying. The results are summarized below.

Add-on SFC Peel Speed Paper Combo (dry- Thickness strength Trial (fpm)Liner-Medium Adhesive lb/msf) (in) (g/in) Observations 1 338 18#-18# C1*2.2 0.055 141 control, standard run 2 62 18#-18# C2-A** 4.1 0.060 22 noimpression lines on back 3 295 18#-18# C2-B*** 5.3 0.057 120 impressionlines on back 4 360 33#-33# C3-A 0.81 0.062 FT 5 360 18#-18# C3-B 0.820.054 FT edge CD warp 7 344 23#-18# C3-C 1.35 0.053 FT 6 344 23#-18# I14.78 0.053 FT some expansion 8 321 23#-18# I2 3.83 0.055 FT filletvisible 9 331 23#-18# I3 4.16 0.058 FT fillet visible 10 321 23#-18# I44.27 0.057 FT visible expansion 11 311 18#-23# I5 5.92 0.056 FT filletvisible 12 300 18#-18# I6 4.92 0.055 FT ran very well in splice, flatsheets *Cross-section of paper seen in FIG. 2 **Cross-section of paperseen in FIG. 3 ***Cross-section of paper seen in FIG. 4

Full Tear (FT) indicates that the peel strength of adhesive hadsufficient strength, and as such the peel strength could not bemeasured. Looking at the data generated, several observations were made.First, the inventive adhesive composition was found to have better peelstrength than the control adhesive and the control adhesive withmicrospheres. In addition, each of the tests using composition I(inventive) were found to have a visible fillet and/or visibleexpansion, and thus it can be concluded that the inventive compositionforms better fillets (shoulders) than without microspheres. As can beseen with control composition C3, for example, the use of a compositionusing a high amylose adhesive without microspheres may lead toundesirable edge cross direction warpage, especially for low weightpaper. Additionally, it was found that the inventive adhesivecomposition may be useful on thinner liner-medium without any warpage,and a high corrugating speed can be used. Due to the expansion of themicrospheres in between the medium and liner and also in the filletsshoulders, heat resistance of the article may be increased due to therigidity and strength of the article, which maintains the medium-linerconfiguration.

As can be seen, Composition I was very successful when used on eachgrade of paper, and particularly successful when used on the lowestgrade of paper liner and medium (Trial 12). This trial was found to runvery well in splice, and gave flat sheets.

What is claimed is:
 1. A method of making an insulative sheet,comprising the steps of: a. providing a substantially planar paper sheethaving a first side and a second side, said first side having any typeof surface to accommodate an insulating component; b. preparing anadhesive composition comprising the steps of: i. combining a highamylose starch component that has an amylose content greater than 50%,an alkaline component, sodium tetraborate, water, and about 0.5 to about5 wet basis weight percent of a plurality of expandable microspheres toform a starch mixture; ii. cooking said high amylose starch mixture toform a cooked starch mixture; iii. adding unmodified starch component tosaid cooked starch mixture; and iv. adding a plurality of expandablemicrospheres to said cooked starch mixture; c. applying said adhesivecomposition to said surface of said first side of said substantiallyplanar paper sheet to form a sheet with an applied adhesive composition;d. applying a second substantially planar paper sheet having a firstside and a second side, said first side having any type of surface toaccommodate an insulating component, to the top surface of the adhesivecomposition; e. heating said sheet with said applied adhesivecomposition to a first temperature of about 180° F. to about 210° F.;and f. heating said sheet with said applied adhesive composition to asecond temperature sufficient to fully cure said adhesive composition.2. The method of claim 1, wherein said high amylose starch component isselected to permit full gelatinization of said cooked starch mixture ata temperature at or greater than the temperature at which saidexpandable microspheres expand.
 3. The method of claim 1, wherein saidunmodified starch is selected to permit full gelatinization of saidcooked starch mixture at a temperature at or greater than thetemperature at which said expandable microspheres expand.
 4. The methodof claim 1, wherein said step of applying said adhesive composition tosaid first side of said substantially flat paper sheet comprisesapplying said adhesive composition such that said plurality ofexpandable microspheres are applied in a configuration selected from thegroup consisting of dots, stripes, waves, checkerboard patterns, anygeneral polyhedron shapes that have substantially flat bases, cylinders,and combinations thereof.
 5. The method of claim 1, wherein said firsttemperature is insufficient to fully cure said adhesive composition. 6.The method of claim 1, wherein said second temperature is about 20° F.to about 40° F. greater than the T_(exp) of said expandablemicrospheres.